There is considerable art relating to reversible variable speed drive mechanisms. Representative of that art are U.S. Pat. Nos. 2,179,933, and 2,889,716. Both of the patents referred to operate on a common principle. A balancing shaft is placed parallel to the drive shaft of an engine. A belt is connected between a pulley on the drive shaft and a pulley on the balancing shaft, so that the drive shaft imparts a rotational motion to the balancing shaft. By adjusting the rotational circumference of one of the pulleys supporting the belt the rotational speed of the balancing shaft can be adjusted relative to the rotational speed of the drive shaft. The drive shaft is coupled to one of the gears of a planetary gear assembly. The balancing shaft is coupled to another of the gears of the planetary gear assembly. By adjusting the relative speeds of the drive shaft and the balancing shaft the output gear of the planetary gear assembly can be made to rotate in either direction or maintain a stationary or neutral position.
These reversible variable speed drive mechanisms have not become widely used in motor vehicles for a number of reasons. One reason is that the configurations known in the art are often not suited for placement under the hood of an automobile. Another reason is that the devices can not be relied upon to maintain a neutral setting when left unattended. The belts used are subject to stretching. As soon as the speed of the balancing shaft is altered relative to the drive shaft by the stretching of a belt movement of the output shaft occurs.